U.S. Pat. No. 4,928,146 issued to Yamada on May 22, 1990, is illustrative of a number of references which show the development of a series of electrostatic images carried on a photoconductive drum with different colored toners at a single development position. See also, U.S. Pat. No. 3,797,930, Tanaka et al, issued Mar. 17, 1974; U.S. Pat. No. 4,275,134, Knechtel, issued Jun. 23, 1981; Japanese Kokai 1-244477 (1989); U.S. Pat. No. 4,728,983, Zwaldo, issued Mar. 1, 1988. A series of four development stations are moved one after another to the development position. Each station develops an image and is replaced by another station as the series of stations is indexed to apply a different color toner to the next image. The series of stations are arranged side-by-side and moved linearly through a position in which the station to be used is aligned with the development position. After or as it is aligned, a cam is rotated to push the entire station toward the development position, generally moving transverse to the motion of the series of stations.
This general approach has the advantage of utilizing only a single development position for applying four different color toners to electrostatic images. This permits the use of development stations whose size and number would prohibit them from being spaced around the periphery of a relatively small photoconductive drum. It thus also permits the use of a small photoconductive drum in multicolor imaging. The use of a small drum has many advantages including reduced expense, reduced size of the apparatus and convenience in cartridge-type replacement.
The structure shown in the prior art requires accurate translational movement of the four stations to maintain the alignment of a relatively long, narrow station with a relatively long, narrow portion of an image member.
Typically, the four development units are positioned on a carriage which carriage in turn is mounted on rails. The carriage is driven on the rails with a chain or belt drive. The rails maintain the alignment of the carriage as it moves, bringing each development unit sequentially into position. However, a chain or belt drive adds substantial complexity and expense to the system and is difficult to assemble and maintain.
U.S. Pat. No. 4,941,018 Kasamura, issued Jul. 10, 1990 shows, in FIG. 27, use of a rack on a development carriage and a pinion connected to a mechanism plate of a printer for indexing toning stations. A rack and pinion approach provides adequate power and a smooth drive for such a structure. The movement of the development carriage is controlled by rails and other extensive guide structure separate from the drive.